There are currently no runtime diagnostic checks for detecting when we have inadvertently missed a call to update_rq_clock() before accessing rq_clock() or rq_clock_task().
The idea in these patches, which came from Peter, is to piggyback on the rq->lock pin/unpin context to detect when we expected (and failed) to see an update to the rq clock. They've already caught a couple of bugs: see commit b52fad2db5d7 ("sched/fair: Update rq clock before updating nohz CPU load"). All the diagnostic code is guarded by CONFIG_SCHED_DEBUG, but there are minimal changes to __schedule() in patch 5 for the !SCHED_DEBUG case. Jan and Sergey, Petr asked that you be Cc'd on this series because of the recent issues with using WARN_ON() in the async printk work. Changes in v2: - Add a check for missing update_rq_clock() before rq_clock_task(). - Address review comments from Yuyang where I messed up the __schedule() ::clock_update_flags manipulation Matt Fleming (7): sched/fair: Update the rq clock before detaching tasks sched/fair: Update rq clock before waking up new task sched/fair: Update rq clock in task_hot() sched: Add wrappers for lockdep_(un)pin_lock() sched/core: Reset RQCF_ACT_SKIP before unpinning rq->lock sched/fair: Push rq lock pin/unpin into idle_balance() sched/core: Add debug code to catch missing update_rq_clock() kernel/sched/core.c | 92 +++++++++++++++++++++------------------- kernel/sched/deadline.c | 10 ++--- kernel/sched/fair.c | 40 +++++++++++------- kernel/sched/idle_task.c | 2 +- kernel/sched/rt.c | 6 +-- kernel/sched/sched.h | 107 ++++++++++++++++++++++++++++++++++++++++------- kernel/sched/stop_task.c | 2 +- 7 files changed, 177 insertions(+), 82 deletions(-) -- 2.9.3